Process of coating or joining articles of tungsten or molybdenum.



' full TO THE GOV .11:

0F THE UNITED STATES OF AMERICA.

c K A. FAHJRENWALD, 01F. CLEVELAND, OHIO, DEDICATED, BY MESNEASSIGNMENTS,

.Nll/IJENT OF THE UNITED STATES OF AMERICA AND TO THE PEOPLE rnoenss orUUA'IJENG: on JOINING ARTICLES or ronesrnn on MOLYBDENUM.

enants,

Ito Drawing.

' Specification of Letters ratent.

Patented Apr. es, mi.

(DEDICATED TO THE PUBLIC.)

To all whom it may concern:

' WALD, a citizen of the United States residing at Cleveland, in thecounty of (iuyahoga and State of Ohio, have invented a certain new anduseful Improvement in Processes of Coating or Joining Articles ofTungsten or Molybdenum, of which the followingis a clear, and exactdescription.

This applicationis made under the act of March 3, 1883, chapter 143 (22Stat. 625) and the invention herein described and claimed may be used bythe Government of royalty thereon. The invention relates to acompositionof matter for use in coating or soldering metals, or coating metals forsoldering urposes. ticularly esigned for he purpose of solderingtungsten, molybdenum, or their alloys, and other metals of like nature;although it is not restricted to use upon such metals only, or tosoldering purposes only, but may be employed with other metals, or forcoating purposes merely, or for any other purpose for which it may beuseful; However, in the following description I shall confine myselfmore especially to the particular functions above mentioned, but withthe proviso thatthis is only one of many uses and the described metalsare only a few of the'many substances to which my invention isapplicable,

On account of the ease of om'dation of tungsten, molybdenum, and thelike metals at high temperatures (say above 600 C.) and because of theirsmall aifinity at ordinary working temperatures for metals or alloys towhich it is desired to unite them, the

soldering or. brazing of metallic masses ofv tungsten and molybdenum,-or their" high Tlie invention is par-'' ture are-desirable. For examplein dental work the securing of a crown in place frequentlynecessitatesthe use of a post for its support, which post is anchored in the root ofthe tooth. This post must be of some metal which shall not react withany substance with which it comes in contact, it must be strong andstiff, it must be substantially permanent, and it should be of verysmall size in order to avoid the necessity for removing too much toothstructure, thereby destroying the foundation. Tungsten, mo-

lybdenum, and their high percentage alloys fulfil all these requirementsexcepting that the dificulty of soldering or otherwise affixing thecompleted crown thereto has greatly impeded their use. In addition thereare a great many occasions where metals of thisnature are useful inchemical, physical and other scientific. apparatus, and in practicalarts.

l[ have discovered that the soldering of these metals can be veryconveniently effected by the emplo ment of a proper flux, the nature ofsaid fl nature and composition of the original metal, and of the a pliedmetal, and of the use to which the w ole is to be put. Such a flux mustpossess afusing point below that of the soldering material and shouldnot be completely volatilized at the working temperature. It shouldreadily v dissolve the metallic oxid coating, present or formed inheating, and should be of such material as to prevent further oxidationduring the soldering operation.v It should produce a clean metallicsurface with which the added alloy or metal will readily unite. Also itmust be of such a nature as not toreact injuriously upon the original,metal as by crystallizingor dissolving it and must be applicable undersuch temperatures and within such a length of time as will not injurethat metal. t In developing the material for this purpose, l[ have foundthat the oxy en salts of the alkali metals form the best uxfordissolving the oxid from the surface of the molybdate by uniting withthe oxid of these metals. I have found that sodium carbonate or betterstill a mixture of the same with fused borax serves very satisfactorilyfor this purpose, though'inany alkali salts will serve. p

' This cleansing flux alone, however, is

hardly suficient, since even with its use it is' very' difficult tocause any of the precious metals, as

gold, silver, palladium, platinum,

or their alloys to unite with molybdenum or tungsten metals or theiralloys under ordinary conditions of manipulation. It can sometimes bedone, but the operation is uncertain and the se'curity of contactimperfect. ,To overcome this difiiculty I .add to application is less tobe feared than in the case of the-metal itself. For operative purposes,however, it is necessary only that some such finely divided metal ormetal salt (either in the combined or uncombined form be added as will apear in' the fused meta '0 condition after t lie flux is applied andmelted;

The use and action of this flux combina- -tion is then essentially asfollows: The

tungsten or molybdenum metals or alloys are heated and dipped into ordrenched with the powdered flux causing a small amount to adhere to thehot surface. Heat in stronger degree is then applied from a blastlamp orblow pipe or other suitable means. As the :temperature is raised, thealkali salt melts, reacts with the surface oxid,

thoroughly cleaning the metal, upon which is simultaneously depositedthe metallic content of the .45

flux, which has also become molten. The

surface thus receives a cleansing and proquired .tectiv'etreatmentpractically simultaneously, and may then be soldered or brazed by addingordinary gold or precious metal rsoldersjin the usualmanner. It is-bestto complete the operation by addin the reamount of solder and meltingdown with the flux. The temperature shouldbe the metal.

maintained below about 1400 C. and even this temperature maintained for.not more than about 30 seconds in the case of ductile tungsten ormolybdenum, since a higher temperature or a, longer time tends to weakenOf course lower. temperatures can safely be maintained for a longer timebut the timefactor is best kept as; low as convenient. i W1th this fluxI have found'it compara-' tivelyv simple ;to unite structural units'oftungsten or molybdenum wires or sheets, and

may contain only gold, so that the gold color may be maintained. If aplatinum color is desired, palladium or platinum may be added, whichalso gives a stronger bond and a joint of higher melting point. Inthismanner pure platinum may be used in extreme cases, although its userequires very delicate manipulation since with temperatures much aboveM00 C. there is danger of crystallization or annealing. Silver alone maybe employed but adheres rather weakly and appears for some unknownreason to ac celerate crystallization, wherefore its use I alone is notrecommended. Palladium alone adheres very strongly and even alloysslightly, but also, when used alone, appears to acceleratecrystallization though when used in company with a preponderance of goldthis deteriorating effect is not observable. Gold alone hascomparatively little atfinity for tungsten or molybdenum and the line ofcontact is rather clearly defined, though it adheres reasonably well forall practical purposes and forms a most beautiul coatin without anyinjury to the metal beneath. .[ts adhesion is improved by the additionof five to ten per cent. of alladium, and without inimical effect so faras observed, and this I consider the most perfect coating. Metals of theplatinum group, or other refractory precious metals, such as iridium forexample, have a marked dissolving'efi'ect, so that if a true alloyedbond is desired one or more of these metals should be present. Othermetals, as copper, may be used in his flux if recautions are observed,which use is sometimes desirable in case a gold-copper or silver-copperalloy is to be attached.

The metallic contact of the flux may vary within very wide limits; Ihave obtained perfect (but very thin) protective coatings with as low astwo per cent. of precious metal in the flux, although I prefer to employa larger proportion. With this flux as a soldering .or brazing medium,it is possible to fasten electrical contact joints, to solder and buildup apparatus and appliances of various forms, to make electricalconnection, and in fact to perform any operation of joining where it ISdesired to solder or braze-tungsten or molybdenum metals or theiralloys; in addition to thev dental uses above'suggested. In the use ofthis flux 1:10

the temperatures employed are not sufi; ciently high to anneal orrecrystallize these metals, so that their elasticity, ductility, tensilestrength and rigidity are not impaired. In the claims heretoannexed theWords alkali salt are intended to embrace either a simple or a compoundsalt or a mixture of salts of several alkalis, and the same may beeither oxygen containing or oxygen free or a mixture of the same exceptwhere specifically recited. Also by the words precious metal containingor precious metal in finely divided form ll mean ,to embrace either themetal occurring in the metallic condition or in the combined conditionas in a precious metal salt.

Having thus described my invention, What I claim is 1. The process ofcoating tungsten or molybdenum or alloys of the same which contains thestep of heating the same in contact with a dry flux consisting largelyof an alkali salt having a finely divided precious metal intimatelymixed therewith.

2. The process of treating tungsten or molybdenum or their alloys whichconsists in covering the same with a'flu'x'containin an alkali salt anda precious metal, and a er- Ward heating the same to a temperature atleast as high as the melting point of the said 1 point of the saidprecious metal, and third adding a soldering metal or alloy of a naturewhich will alloy with said precious metal.

In testimony whereof, I hereunto afix my signature.

' FRANK A. FAHRENWALJD.

